This invention relates to a force multiplication system for a brake cylinder or the like and more particularly to such a force multiplication system employing a force lever that is only activated following engagement of the brake shoe with the object to be braked, such as a railway vehicle wheel.
The prior art includes systems of this type, e.g., the one indicated in the Utility Model Kokai No. 59-132467. An outline of this system of the prior art is shown in FIG. 6, and it will be explained first. In the FIG., 31 is the cylinder part, 32 is the push rod, 33 is the lever, 34 is the brake shoe and 35 is the wheel. When the compressed air is fed into the cylinder part 31 via the inlet-outlet 31a, the piston 31c moves to the left in the figure against the resistance of the return spring 31b. In this manner, the lever 33 moves around the fulcrum pin 33b in the counter-clockwise direction via the piston rod 31d and the coupling pin 33a. As a result of this movement of the lever 33, the push rod 32 is driven to the left via the space adjuster 32b located on the push rod 32 which is engaged with the middle part of the lever 33. This driving force is increased as a function of the lever ratio of the lever 33, and it strongly presses the brake shoe 34 to the wheel 35.
When the compressed air in the cylinder part 31 is discharged from the inlet-outlet 31a, the piston 31c moves to the right as a result of the reaction force of the return spring 31b, and consequently, the lever 33, the push rod 32, the brake shoe 34, etc., return to their original positions shown in the figure.
In the brake system of the prior art described above, if the brake shoe 34, by engagement with push rod 32, moves forward toward the side of the wheel 35, and performs the braking action, an increase of the braking force exerted by the lever 33 is required only when the brake shoe 34 touches the wheel 35. Nevertheless, the push rod 32 is always driven via the lever 33 at the cylinder part 31, even prior to brake shoe/wheel engagement. If the stroke required to move the push rod 32 is S.sub.1, the stroke required at the time of braking is S.sub.2, and the lever ratio is .alpha., the total stroke of the piston 31c of the cylinder part 31 becomes (S.sub.1 +S.sub.2) (.alpha.), and the stroke multiplied by the lever ratio of the push rod 32 is necessary. Therefore, the piston 31c of cylinder part 31 has an unnecessarily large stroke, and the cylinder part 31 therefore must be large in size to accommodate such a large stroke, which is a problem.